ABSTRACT The autoimmune disease juvenile idiopathic arthritis (JIA), which causes joint, eye, and bone damage and chronic pain, is the most common chronic childhood disease in the United States. Joint fluid from JIA patients contains large numbers of macrophage immune cells, and macrophage secretion of inflammatory factors drives the disease. Current therapies for JIA block this inflammatory signaling but do not discriminate between disease- associated inflammatory signaling and the normal immune response to infection. Therefore, suppression of an- timicrobial immunity is a severe side effect of these existing therapies. We have discovered a signaling mecha- nism through the protein LynA that is required for hypersensitive inflammatory signaling by macrophages, but is not strictly required for pathogen recognition. We have now also generated the first LynA-/- mice and propose to test whether the LynA regulatory pathway has promise as a novel therapeutic target, to specifically suppress inflammatory macrophage signaling without suppressing the immune system generally. Our long-term goal is to develop new therapeutic approaches targeted specifically to pathological macrophages. To evaluate the trans- lational potential of our signaling discovery, we aim to test the role of LynA in isolated macrophages, in mouse inflammatory arthritis, in infection, and in samples from human JIA patients. More specifically, we propose to: 1) Examine the effect of LynA deletion in macrophages: We will use novel LynA-/- mice developed recently in our laboratory to test the independent contributions of LynA to signaling in bone-marrow-derived macrophages. We predict that LynA-/- macrophages will have blunted responses to small stimuli but normal responses to large, pathogen-mimetic stimuli. 2) Examine the role of LynA in mouse inflammatory arthritis and infection: We will assess the progression of inflammatory arthritis and fungal and bacterial infections in wild-type and LynA-/- mice. We will also analyze markers of macrophage function and test signaling responses in splenic and synovial mac- rophages to assess the role of LynA in inflammation. We predict that LynA-/- mice will develop less severe arthritis than wild-type mice but respond normally to infection. 3) Test inflammation-driven LynA upregulation and signal- ing in human macrophages: We hypothesize that, as in mice, inflammation in JIA-affected joints induces LynA upregulation in human macrophages. We will test whether synovial fluid from JIA patients induces LynA upreg- ulation and macrophage hypersensitivity and whether this pathological function is suppressed by knocking down LynA expression. We predict that JIA synovial fluid will induce upregulation of LynA in human macrophages, leading to hypersensitive signaling. This project will benefit from our expertise in macrophage signaling and close collaborations with the research-oriented Pediatric Rheumatology Clinic and other investigators in the Center for Immunology at the University of Minnesota. These studies will establish the feasibility of targeting LynA to de- velop safer, targeted treatment options for JIA and other macrophage-driven inflammatory diseases.